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  Optical system comprising an fm source and a spectral reshaping elementUSPTO Application #: 20060029358Title: Optical system comprising an fm source and a spectral reshaping element Abstract: In one form of the present invention, there is provided a fiber optic communication system comprising: an optical signal source adapted to receive a base binary signal and produce a first signal, said first signal being frequency modulated; and an optical spectrum reshaper adapted to reshape the first signal into a second signal, said second signal being amplitude modulated and frequency modulated; characterized in that: the frequency characteristics of said first signal, and the optical characteristics of said optical spectrum reshaper, being such that the frequency characteristics of said second signal are configured so as to increase the tolerance of the second signal to dispersion in a transmission fiber. In another form of the present invention, there is provided an optical transmitter comprising: a frequency modulated source for generating a first frequency modulated signal, and an amplitude modulator for receiving the first frequency modulated signal and for generating a second amplitude and frequency modulated signal. In another form of the present invention, there is provided a method for transmitting an optical signal through a transmission fiber comprising: receiving a base binary signal; operating an optical signal source using the base binary signal to produce a first signal, said first signal being frequency modulated; passing the frequency modulated signal through an optical spectrum reshaper so as to reshape the first signal into a second signal, said second signal being amplitude modulated and frequency modulated; the frequency characteristics of said first signal, and the optical characteristics of said optical spectrum reshaper, being such that the frequency characteristics of said second signal are configured so as to increase the tolerance of the second signal to dispersion in a transmission fiber; and passing the second signal through a transmission fiber. In another form of the present invention, there is provided a method for transmitting a base signal, comprising: using the base signal to produce a frequency modulated signal; and providing an amplitude modulator for receiving the frequency modulated signal and for generating an amplitude and frequency modulated signal. (end of abstract) Agent: Mark J. Pandiscio Pandiscio & Pandiscio, P.C. - Waltham, MA, US Inventors: Daniel Mahgerefteh, Yasuhiro Matsui, Xueyan Zheng, Bart Johnson, Duncan Walker, Parviz Tayebati USPTO Applicaton #: 20060029358 - Class: 386033000 (USPTO) Related Patent Categories: Television Signal Processing For Dynamic Recording Or Reproducing, Processing Of Color Television Signal For Dynamic Recording Or Reproducing, Compressing When Recording Or Decompressing When Reproducing The Patent Description & Claims data below is from USPTO Patent Application 20060029358. Brief Patent Description - Full Patent Description - Patent Application Claims
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS [0001] This patent application: [0002] (i) is a continuation-in-part of pending prior U.S. patent application Ser. No. 10/289,944, filed Nov. 6, 2002 by Daniel Mahgerefteh et al. for POWER SOURCE FOR A DISPERSION COMPENSATION FIBER OPTIC SYSTEM (Attorney's Docket No. TAYE-59474-00006); [0003] (ii) is a continuation-in-part of pending prior U.S. patent application Ser. No. 10/308,522, filed Dec. 3, 2002 by Daniel Mahgerefteh et al. for HIGH-SPEED TRANSMISSION SYSTEM COMPRISING A COUPLED MULTI-CAVITY OPTICAL DISCRIMINATOR (Attorney's Docket No. TAYE-59474-00007); [0004] (iii) is a continuation-in-part of pending prior U.S. patent application Ser. No. 10/680,607, filed Oct. 6, 2003 by Daniel Mahgerefteh et al. for FLAT DISPERSION FREQUENCY DISCRIMINATOR (FDFD) (Attorney's Docket No. TAYE-59474-00009); [0005] (iv) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/548,230, filed Feb. 27, 2004 by Yasuhiro Matsui et al. for OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL RESHAPING ELEMENT (Attorney Docket No. TAYE-31 PROV); [0006] (v) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/554,243, filed Mar. 18, 2004 by Daniel Mahgerefteh et al. for FLAT CHIRP INDUCED BY FILTER EDGE (Attorney Docket No. TAYE-34 PROV); [0007] (vi) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/566,060, filed Apr. 28, 2004 by Daniel Mahgerefteh et al. for A METHOD OF TRANSMISSION USING PARTIAL FM AND AM MODULATION (Attorney Docket No. TAYE-37 PROV); [0008] (vii) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/567,737, filed May 3, 2004 by Daniel Mahgerefteh et al. for ADIABATIC FREQUENCY MODULATION (AFM) (Attorney Docket No. TAYE-39 PROV); [0009] (viii) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/569,769, filed May 10, 2004 by Daniel Mahgerefteh et al. for FLAT CHIRP INDUCED BY AN OPTICAL FILTER EDGE (Attorney Docket No. TAYE-40 PROV); [0010] (ix) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/569,768, filed May 10, 2004 by Daniel Mahgerefteh et al. for METHOD OF TRANSMISSION USING PARTIAL FM AND AM MODULATION (Attorney's Docket No. TAYE-41 PROV); [0011] (x) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/621,755, filed Oct. 25, 2004 by Kevin McCallion et al. for SPECTRAL RESPONSE MODIFICATION VIA SPATIAL FILTERING WITH OPTICAL FIBER (Attorney's Docket No. TAYE-47 PROV); and [0012] (xi) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/629,741, filed Nov. 19, 2004 by Yasuhiro Matsui et al. for OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL RESHAPING ELEMENT (Attorney's Docket No. TAYE-48 PROV). [0013] The eleven above-identified patent applications are hereby incorporated herein by reference. FIELD OF THE INVENTION [0014] This invention relates to signal transmissions in general, and more particularly to the transmission of optical signals and electrical signals. BACKGROUND OF THE INVENTION [0015] The quality and performance of a digital fiber optic transmitter is determined by the distance over which the transmitted digital signal can propagate without severe distortions. The bit error rate (BER) of the signal is measured at a receiver after propagation through dispersive fiber and the optical power required to obtain a certain BER, typically 10.sup.-12, called the sensitivity, is determined. The difference in sensitivity at the output of the transmitter with the sensitivity after propagation is called dispersion penalty. This is typically characterized the distance over which a dispersion penalty reaches a level of .about.1 dB. A standard 10 Gb/s optical digital transmitter, such as an externally modulated source can transmit up to a distance of .about.50 km in standard single mode fiber at 1550 nm before the dispersion penalty reaches the level of .about.1 dB, called the dispersion limit. The dispersion limit is determined by the fundamental assumption that the digital signal is transform limited, i.e. the signal has no time varying phase across its bits and has a bit period of 100 ps, or 1/(bit rate). Another measure of the quality of a transmitter is the absolute sensitivity after fiber propagation. [0016] Three types of optical transmitters are presently in use in prior art fiber optic systems: (i) directly modulated laser (DML), (ii) Electroabsorption Modulated Laser (EML), and (iii) Externally Modulated Mach Zhender (MZ). For transmission in standard single mode fiber at 10 Gb/s, and 1550 nm, it has generally been assumed that MZ modulators and EMLs can have the longest reach, typically reaching 80 km. Using a special coding scheme, referred to as phase shaped duobinary, MZ transmitters can reach 200 km. On the other hand, directly modulated lasers (DML) reach <5 km because their inherent time dependent chirp causes severe distortion of the signal after this distance. [0017] By way of example, various systems for long-reach lightwave data transmission (>80 km at 10 Gb/s) through optical fibers which increase the reach of DMLs to >80 km at 10 Gb/s in single mode fiber are disclosed in (i) U.S. patent application Ser. No. 10/289,944, filed Nov. 6, 2002 by Daniel Mahgerefteh et al. for POWER SOURCE FOR A DISPERSION COMPENSATION FIBER OPTIC SYSTEM (Attorney's Docket No. TAYE-59474-00006); (ii) U.S. patent application Ser. No. 10/680,607, filed Oct. 6, 2003 by Daniel Mahgerefteh et al. for FLAT DISPERSION FREQUENCY DISCRIMINATOR (FDFD) (Attorney's Docket No. TAYE-59474-00009); and (iii) U.S. patent application Ser. No. 10/308,522, filed Dec. 3, 2002 by Daniel Mahgerefteh et al. for HIGH-SPEED TRANSMISSION SYSTEM COMPRISING A COUPLED MULTI-CAVITY OPTICAL DISCRIMINATOR (Attorney's Docket No. TAYE-59474-00007); which patent applications are hereby incorporated herein by reference. The transmitter associated with these novel systems is sometimes referred to as a Chirp Managed Laser (CML).TM. by Azna LLC of Wilmington, Mass. In these new systems, a Frequency Modulated (AFM) source is followed by an Optical Spectrum Reshaper (OSR) which uses the frequency modulation to increase the amplitude modulated signal and partially compensate for dispersion in the transmission fiber. In one embodiment, the frequency modulated source may comprise a Directly Modulated Laser (DML). The Optical Spectrum Reshaper (OSR), sometimes referred to as a frequency discriminator, can be formed by an appropriate optical element that has a wavelength-dependent transmission function. The OSR can be adapted to convert frequency modulation to amplitude modulation. [0018] In the novel system of the present invention, the chirp properties of the frequency modulated source are separately adapted and then further reshaped by configuring the OSR to further extend the reach of a CML.TM. transmitter to over 250 km on standard single mode fiber at 10 Gb/s and 1550 nm. The novel system of the present invention combines, among other things, selected features of systems described in (i) U.S. Provisional Patent Application Serial No. 60/548,230, filed Feb. 27, 2004 by Yasuhiro Matsui et al. for entitled OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL RESHAPING ELEMENT (Attorney Docket No. TAYE-31 PROV); (ii) U.S. Provisional Patent Application Ser. No. 60/554,243, filed Mar. 18, 2004 by Daniel Mahgerefteh et al. for FLAT CHIRP INDUCED BY FILTER EDGE (Attorney Docket No. TAYE-34 PROV); (iv) U.S. Provisional Patent Application Ser. No. 60/566,060, filed Apr. 28, 2004 by Daniel Mahgerefteh et al. for, A METHOD OF TRANSMISSION USING PARTIAL FM AND AM MODULATION (Attorney Docket No. TAYE-37 PROV); (iv) U.S. Provisional Patent Application Ser. No. 60/567,737, filed May 3, 2004 by Daniel Mahgerefteh et al. for ADIABATIC FREQUENCY MODULATION (AFM) (Attorney Docket No. TAYE-39 PROV); (v) U.S. Provisional Patent Application Ser. No. 60/569,769, filed May 10, 2004 by Daniel Mahgerefteh et al. for FLAT CHIRP INDUCED BY AN OPTICAL FILTER EDGE (Attorney Docket No. TAYE-40 PROV), which patent applications are hereby incorporated herein by reference. SUMMARY OF THE INVENTION [0019] This invention provides an optical spectrum reshaper (OSR) which works in tandem with a modulated optical source which, by modifying the spectral properties of the modulated signal, results in extending the optical transmission length well beyond the dispersion limit. The OSR can be defined as a passive optical element that imparts an optical frequency dependent loss and frequency dependent phase on an input optical signal. This invention also provides a modulated laser source and an optical spectrum reshaper system that increases tolerance to fiber dispersion as well as converting a partially frequency modulated signal into a substantially amplitude modulated signal. [0020] The optical spectrum reshaper (OSR) may be a variety of filters such as a Coupled Multicavity (CMC) filter to enhance the fidelity of converting a partially frequency modulated signal into a substantially amplitude modulated signal. The OSR may also partially compensate for the dispersion of the fiber. In one embodiment of the present invention, a modulated laser source may be provided that is communicatably coupled to an optical filter where the filter is adapted to lock the wavelength of a laser source as well as converting the partially frequency modulated laser signal into a substantially amplitude modulated signal. [0021] In one form of the present invention, there is provided a fiber optic communication system comprising: [0022] an optical signal source adapted to receive a base binary signal and produce a first signal, said first signal being frequency modulated; and [0023] an optical spectrum reshaper adapted to reshape the first signal into a second signal, said second signal being amplitude modulated and frequency modulated; [0024] characterized in that: [0025] the frequency characteristics of said first signal, and the optical characteristics of said optical spectrum reshaper, being such that the frequency characteristics of said second signal are configured so as to increase the tolerance of the second signal to dispersion in a transmission fiber. [0026] In another form of the present invention, there is provided an optical transmitter comprising: [0027] a frequency modulated source for generating a first frequency modulated signal, and [0028] an amplitude modulator for receiving the first frequency modulated signal and for generating a second amplitude and frequency modulated signal. [0029] In another form of the present invention, there is provided a method for transmitting an optical signal through a transmission fiber comprising: receiving a base binary signal; [0030] operating an optical signal source using the base binary signal to produce a first signal, said first signal being frequency modulated; [0031] passing the frequency modulated signal through an optical spectrum reshaper so as to reshape the first signal into a second signal, said second signal being amplitude modulated and frequency modulated; [0032] the frequency characteristics of said first signal, and the optical characteristics of said optical spectrum reshaper, being such that the frequency characteristics of said second signal are configured so as to increase the tolerance of the second signal to dispersion in a transmission fiber; and [0033] passing the second signal through a transmission fiber. [0034] In another form of the present invention, there is provided a method for transmitting a base signal, comprising: [0035] using the base signal to produce a frequency modulated signal; and [0036] providing an amplitude modulator for receiving the frequency modulated signal and for generating an amplitude and frequency modulated signal. [0037] In another form of the present invention, there is provided a fiber optic communication system comprising: [0038] an optical signal source adapted to produce a frequency modulated signal; and [0039] an optical spectrum reshaper adapted to convert the frequency modulated signal into a substantially amplitude modulated signal; characterized in that: [0040] the operating characteristics of the optical signal source and the optical characteristics of the optical spectrum reshaper combine to compensate for at least a portion of a dispersion in an optical fiber. [0041] In another form of the present invention, there is provided a method for transmitting an amplitude modulated signal through a fiber comprising: [0042] providing a laser and providing a filter having selected optical characteristics; [0043] inputting the amplitude modulated signal into the laser, and operating the laser, so as to generate a corresponding frequency modulated signal; [0044] passing the frequency modulated signal through the filter so as to generate a resulting signal and passing the resulting signal into the fiber; [0045] the laser being operated, and the filter being chosen, such that the resulting signal is configured to compensate for at least a portion of the dispersion in the fiber. [0046] In another form of the present invention, there is provided a fiber optic communication system comprising: [0047] an optical signal source adapted to produce a first signal, said first signal being frequency modulated; and [0048] an optical spectrum reshaper adapted to convert said first signal into a second signal, said second signal being amplitude modulated and frequency modulated; [0049] characterized in that: [0050] the frequency characteristics of said first signal, and the optical characteristics of said optical spectrum reshaper, being such that the frequency characteristics of said second signal are configured so as to extend the distance said second signal can travel along a fiber before the amplitude characteristics of said second signal degrade beyond a given amount. [0051] In another form of the present invention, there is provided a fiber optic communication system comprising: [0052] a module adapted to receive a first signal and convert said first signal into a second signal, said second signal being amplitude modulated and frequency modulated; [0053] characterized in that: [0054] the frequency characteristics of said second signal are configured so as to extend the distance said second signal can travel along a fiber before the amplitude characteristics of said second signal degrade beyond a given amount. [0055] In another form of the present invention, there is provided a system adapted to convert a first signal into a second signal, said second signal being amplitude modulated and frequency modulated; [0056] the improvement comprising: [0057] tailoring the frequency characteristics of said second signal so as to extend the distance said second signal can travel along a fiber before the amplitude characteristics of said second signal degrade beyond a given amount. [0058] In another form of the present invention, there is provided a fiber optic communication system comprising: [0059] an optical signal source adapted to receive a base signal and produce a first signal, said first signal being frequency modulated; and [0060] an optical spectrum reshaper adapted to convert said first signal into a second signal, said second signal being amplitude modulated and frequency modulated; [0061] characterized in that: [0062] the frequency characteristics of said first signal, and the optical characteristics of said optical spectrum reshaper, being such that the frequency characteristics of said second signal are configured so as to extend the distance said second signal can travel along a fiber before the amplitude characteristics of said second signal degrade beyond a given amount. [0063] In another form of the present invention, there is provided a fiber optic communication system comprising: [0064] an optical signal source adapted to produce a first signal, said first signal being frequency modulated; and [0065] an optical spectrum reshaper adapted to convert said first signal into a second signal, said second signal being amplitude modulated and frequency modulated; [0066] characterized in that: [0067] the frequency dependent loss of the optical spectrum reshaper is adjusted to increase the dispersion tolerance of the second signal. Continue reading... Full patent description for Optical system comprising an fm source and a spectral reshaping element Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Optical system comprising an fm source and a spectral reshaping element patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. 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